There are many known types of welding-type power supplies that provide welding type power. Welding type power, as used herein, refers to power suitable for electric arc welding, plasma arc cutting or induction heating. Welding-type power supply, as used herein, refers to a power supply that can provide welding type power. Welding type systems are used to perform a variety of processes and used in a variety of settings. Welding-type system, as used herein, is a system that can provide welding type power, and can include control and power circuitry, wire feeders, and ancillary equipment.
Some welding type systems include a preregulator which provides a dc bus, followed by an inverter based output circuit. The preregulator conditions the input power, and provides a known dc bus. The inverter based output circuit receives the bus and provides the welding type power as an output. One successful design includes a boost circuit as part of the preregulator, and the output circuit includes an inverter, transformer, rectifier and output inductor. This type of welding type power supply is described in U.S. Pat. No. 6,987,242 (Geissler). Other welding type power supplies that have inverter based output circuits include U.S. Pat. No. 6,115,273 (Geissler) and Patent Publication 20090230941 (Vogel), all three of which are owned by the owner of this patent, and all three of which are hereby incorporated by reference. Other welding type power supplies include additional stages, or use other topologies for each stage (such as a buck preregulator, a combined rectifier-boost preregulator, a chopper instead of or following the inverter, a second inverter following the first inverter, etc.
Inverter based output circuits offer many advantages, but they do have some drawbacks. First, the switches and diodes used in an inverter circuit can fail, particularly when exposed to higher than rated voltages. Clamping voltages is known, but can result in excess losses. Also, commutating switches and diodes can create excess heat. U.S. Pat. No. 6,801,443 returned the entire clamp energy back into the output in one single switching event.
Most welding type power supplies include and output inductor. Starting the welding process can be difficult, particularly with a large output inductor, because the inductor must be “charged” before welding can be preformed. This can be made more difficult during starting because of the higher than usual arc voltage. Past welding type power supplies have started by a “crowbar” of the bus but that can stress components.
Accordingly, a welding type power supply with an inverter output circuit that is clamped in an efficient manner is desirable. Preferably, such welding type power supply would also provide for efficient commutations of devices and will provide for efficient starting of the weld process.